An AC plasma display panel of dot matrix type includes a plurality of row electrodes disposed in parallel each other and a plurality of column electrodes disposed in parallel each other to form a matrix with the row electrodes. In the matrix, a plurality of discharge spaces each corresponding to a pixel are formed. A plurality of the row and column electrodes cross each other in a right angle. Each crossing point forms a pixel. The row electrodes are composed of two groups, one is that of scanning electrodes and the other is that of common electrodes.
In operation, the common electrodes are supplied with maintaining pulses periodically for maintaining discharge in the pixels, respectively. On the other hand, the scanning electrodes are supplied with maintaining pulses periodically in the same timing but different timing with the maintaining pulses, respectively. Each of the scanning electrodes is also supplied with a scanning pulse and an extinguishing pulse in some timing which comes in turn. The column electrodes are supplied with data pulses of positive in accordance with light emission data in the same timing as the scanning pulses supplied to the scanning electrodes. One field for displaying one frame is divided to a plurality of sub-fields, and light emission time by discharge in each sub-field is controlled to display gradation of brightness of the pixels. If one field is divided to six sub-fields, gradation of brightness of the pixels becomes 2.sup.6 =64 grades. The gradation of 64 grades in each pixel can be realized by selecting one state from light emission and non-light emission in each sub-field. This conventional method is described on pages 13 to 18 of "The technical report of the television institute" published on Nov. 22, 1984.
According to the conventional method for driving a plasma display panel, however, there is a disadvantage in that light emission efficiency of pixels is relatively low, because no light emission times are long compared with light emission times in one field. It is supposed that one field is divided to six sub-fields each having equal sub-field time T.sub.s, and the six sub-fields have different light emission times of T, T/2, T/4, T/8, T/16 and T/32, respectively. If the first emission time T is equal to the sub-field time T.sub.s, the maximum light emission efficiency becomes (1+1/2+1/4+1/8+1/16+1/32)T/6T.sub.s =0.328, that is 32.8%. Therefore, remaining time which is 67.2% of the whole field time is consumed idly.